This chart displays the current beacon strength of each access point compared with an earlier snapshot. The current beacon strength is displayed in purple, the snapshot in light-blue, and the difference in olive green. The Y-axis reports the signal strength as a signal quality (0 - 100%) -- where a maximum signal is assumed to be -20 dBm and the dissociation signal is -85 dBm (http://www.ces.clemson.edu/linux/dbm-rssi.shtml). We find this more intuitive than reporting a RSSI in dBm or mWatt. If you would also like to know the signal strength in dBm then this is reported in the grid above the chart.
The Differential display can be used to view small (or large) changes in beacon strength over time. Here's how it works -- when the application is launched then a 'snapshot' of the beacon strengths is taken -- these are the gray bars. These bars are static and do not change. The green bars show the current beacon strengths, and the blue bars represent the differences between the snapshots and the current beacon strengths.
Whenever you wish to update the snapshot of beacon strengths that is compared against the current beacon strengths: right-click the mouse button on top of the chart to access a small, popup menu. By selecting 'Refresh Snapshot' then the snapshot is updated.
Finally, by checking/unchecking BSSIDs in the grid you can tailor this view to better focus on the access points you are most interested in monitoring. For example, for the figure below we first unchecked all access points (in the grid) and then checked the three we were most interested in -- pharlink_2, dlink and netstress.
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